For recording on recording media such as papers, etc., by writing instruments (e.g., a fountain pen, a felt pen, etc.), there have hitherto been used inks, which are solutions of various dyes dissolved in water or organic solvents.
It is also known that in a so-called ink-jet recording system wherein recording is performed by ejecting a recording liquid in a recording head through discharging orifices by vibration of piezo oscillators, the electrostatic attraction caused by the application of a high voltage, etc., recording liquids obtained by dissolving various dyes in water or organic solvents are used. However, of the ink-jet recording liquid, more rigorous performance characteristics are requested than for a general writing ink for writing instruments such as a fountain pen, a felt pen, etc.
In such a recording system recording is performed by ejecting droplets of a recording liquid (a recording ink) onto a recording media, such a recording liquid is fundamentally composed of a recording agent (a dye or a pigment) and a liquid medum (water, an organic solvent or a mixture of them) for dissolving or dispersing the recording agent and, if necessary, various additives are added to the recording liquid.
Preferred conditions required for this kind of recording liquid are as follows:
(1) The recording liquid possesses liquid properties (viscosity, surface tension, electric conductivity, etc.) matching the discharging conditions (a driving voltage and a driving frequency of a piezo electric element, the form and material of orifices, the diameter of orifices, etc.). PA1 (2) The recording liquid can be stored for a long period of time and does not cause clogging of orifices during use. PA1 (3) The recording liquid is quickly fixed onto recording media such a papers, films, etc., the outlines of the resulting ink dots are smooth, and blotting of the dotted ink is minimized. PA1 (4) The recorded image of the recording liquid has a clear color tone and a high density. PA1 (5) The recorded image of the recording liquid is excellent in water resistance and light resistance. PA1 (6) The recording liquid does not attack or erode surrounding materials (the container for the recording liquid, connecting tubes for discharging orifices, sealants, etc.). PA1 (7) The recording liquid has no unpleasant smell, toxicity, inflammability, etc.
As this kind of recording liquid, there are known solutions or dispersions of various dyes or pigments in aqueous or nonaqueous solvents as disclosed, for example, in Jaspanese Patent Publication Nos. 8361/1975, 40484/1976, 13126/1977 and 13127/1977, and Unexamined Published Japanese Patent Application No. 95008/1975. However, none of these prior art recording liquids are completely satisfactory since they do not possess all of the features (1) to (7) required for ideal recording liquids.
Recording liquids are basically composed of dyes and solvents therefor, and their performance depends largely upon the inherent properties of the dyes. Therefore, choosing dyes that provide recording liquids with the desired features (1) to (7) is a very important factor in the art concerned.
Trisazo compounds known as black dyes have the following formulae: ##STR3##
Compounds known as blue and green dyes have the following formulae, respectively: ##STR4##
These dyes, however, are unsatisfactory for use in recording liquids and further improvements are desirable with respect to solubility, light resistance, stability in extended storage, and stability during discharging.